Let me explore a bit some ideas about color palettes.
You can not have just 1 color when you design a visual element, because, of course, you need a difference in contrast so we can perceive text or any image for that matter.
2. One but two
One color palette could also be thought of as giving a kid the choice of what crayon to use. He can choose just 1, but you also have the white of the paper as the default canvas.
So you can also a palette of 1 color that could not be black. You can have a dark blue for texts and your logo and buttons.
3. One but many
If you control the pressure of your crayon you will find that you can have different tones of the color you choose.
We can have what is called a monochromatic palette. This opens the door to how we can dissect a color solid.
Here is one HSV solid. A cone with a chromatic circle at the top, black on the bottom, and a gradient to the center.
I marked a cross-section of 1 magenta hue. Now you have at your disposal:
- The color you choose
- A gradient of colors from white to your color.
- White and black, and all the grays
- Gradients from the saturated magenta to white, saturated magenta black,
and saturated magenta to any gray.
4. Two as two
So, we have established that we need at least two colors. That is the minimum and it is perfectly fine. You can have a business card on just 1 ink on white or on colored paper, or a website with one color and white or a pastel color for example.
There are many principles to explore regarding color.
One is that you can have 3 colors in different proportions. That is called a 60-30-10 meaning
- 60% one main distinctive color
- 30% one secondary color
- 10% one accent color
In some cases that could include the background color, let's say white, or a pastel creamy color. Or you can think about this besides white, which will give you a 4 color palette, or 5 if you include black.
Or many, if you include gradients between the unsaturated colors to your chosen colors.
But a website that wanted to have a minimalistic approach, could only use black or white, or black and white and one additional color.
Nothing stops you from using only black and white.
I am not addressing the "contrast problems" that is an entire new question.